Mill department control



Fgj.

y 19383 F. MARQUART. 2,124,518

MILL DEPARTMENT CONTROL Filed. Jan. 2, 1956 2 Sheets-Sheet l bwentafl:FewA/K Mnecguqe July 19, 1938 F. MARQUART 2,124,513

MILL bEPAiRTMENT CONTRQL Filed Jan. 2, 1936 i- 2 Sheets-Sheet 2 PatentedJuly 19.1938 V I UNITED STATES PATENT OFFICE MILL DEPARTMENT CONTROLFrank Marquart, Cleveland, Ohio, assignor to The American Steel and WireCompany of New Jersey, a corporation oi New Jersey Application January2, 1986, Serial No. 57,300

I 2 Claims. (01. Bil-31.1)

This invention is concerned with the operation In addition, thedepartment includes other elecoi continuous mills 01' the type whichincludesa trical equipment. Each of these small mills is plurality oftandem roll-stands each provided considered a unit and is of the typeinitially dewith an electric driving motor, when they are scribed. Thatis to say, each of these units in- 5 included as a group of two or morein a mill cludes a plurality of tandem roll-stands. Fur- 5 department,thermore, these mills are operated as units, each Such a mill may beused to reduce metal strip, working on separate lengths of strip. thestrip passing from one roll-stand to anotherf It follows from the abovethat the Wardin succession. It is obvious that each successive Leonardsystem is not applicable as a medium roll-stand must be run at aslightly higher speed of control for these mills, since its use would 10to compensate for the elongation of the metal entail the provision of amotor-generator set for strip, the motors powering these stands beingeach of the units or mills, and this would necescommonly providedwithcontrolling rheostats to sitate such a large outlay of money as to be anprovide the required adjustments. The strip economic impossibility.Furthermore, the other must be manually threaded through the variouselectrical equipment, such as coilers, slitters, coil- 15 stands beforerolling operations can commence. ing machines, craneaand other devicespowered This requires the Operation ofthe ar ou S a d by electricalmotors, must be provided with suitat speeds that are sufilciently slowto prevent able current and this would necessitate still an accidents.When the strip has once been threadother motor-generator set over andabove those ed the speeds of all the roll-stands must be required forthe various mills.

accelerated to normal rolling speeds which are Because of the abovedescribed conditions preconsiderably faster than the speeds requireddurvailing in oldmn a d th r il departing threading. Obviously thisacceleration must ments, including relatively large numbers of elecbeaccomplished so that the speed ratios between trlcally powered units, asingle large motor-genthe various stands do not change. There are eratorset is provided thatis of sumcient capacity 25 several ways ofaccomplishing what has just been to electrically power the entiredepartment. It described, follows that the output of thismotor-generator In the case of strip hot-mills which are so large setcannot be varied as demanded by the Wardas to constitute a complete milldepartment the Leonard system because this would not only con- 39Ward-Leonard system is commonly used. In this trol the speed of one millbut would also affect system the power for the armatures and fields ofall of the other mills and electrical equipment" the motors driving thevarious roll-stands is proincluded by the department. vided by amotor-generator set that receives its Since all the mills in suchdepartments are power from some outside source. This is ecopowered bythe same motor-generator set, it is 85 nomically practical because thedemands of such necessary to provide some means for simultaa mill are sogreat. This motor-generator set neously varying the speeds of the motorsof each does not supply power to any electrical equipment mill fromthreading to full rolling speeds withother than the mill motors. Thespeeds of the out afiecting the motors of the other mills. Herevariousmotors are controlled by the individual tofore, this has been sometimesdone by prorheostats with which they are equipped to effect viding alarge heavy master rheostat for each 40 the compensation required by theelongation of of the mills. In each mill one of these master the work,and the speeds of all the motors may rheostats is in series with theshunt fields of the be simultaneously varied by varying the outputmotors of that mill and with the rheostats which of the motor-generatorset, this being possible individually control the speeds of that millsbecause there is no other electrical equipment to motors. This workssatisfactorily when all of 45 be aifected. This system is also used inthe case the roll stands in each of the mills are utilized of the hugetandem cold-mills now used to produring rolling. However, it isfrequently necesduce very wide metal strip. sary to use less than all ofthe stands included The above system is not suited for application byone of these mills. In such instances the to continuous mills such asareused, for instance, motors of some of the stands are disconnected, 50to cold-roll narrow metal strip. This product is and this removes theirindividual rheostats from commonly produced in what is called thecoldtheir normal series connection with their master rolling departmentof a mill. These mills are rheostat. naturally rather small, and acold-rolling depart- Now, consequently, the settings for the threadmenttherefore includes a number of such mills. ing and iull rolling speedsof the master rheo- 55.

- stat are "no longer" the same, and accidents are very apt to occur-inthat the rollers may forget to adjust the resistance of the masterrheostat to maintain the correct operating speed of the mill.

Sometimes casualties are suffered bythe rollers, and it is even possibleto put an entire mill out of operation. In spite of these defects thissystem now being described has been in common use in departments. of thecharacter underdiscussion. g

The primary object of the present invention is,

to provide a control that is as tool-proof and Figure 1 includes threecold-rolling mills A, B-

and C. Also, it includes a slitter D. The mill A consists of five tandemroll-stands I, which are individually driven by electric motors 2through the usual gear boxes 3. The mill is provided at one end with acoiler 4 that handles thework leaving the last stand inthe usual manner.The operating requirements of this mill have already been generallyoutlined.

The mill B includes only three roll-stands 5, each individually drivenby electric motors 6 through gear boxes I. This mill is also providedwith a coiler 8.

The'mill C is exactly like the mill B, the rollstands being numbered 9,the motors III and the gear boxes I l.

The slitter D is conventional and need not be described in detailexcepting to mention that it is powered by an electric motor I 2.

All of these mills are units in themselves, and the slitter D is also aunit. Each of these units is entirely independent of the others and mustbe operated and controlled independently. For reasons already describedthe department is provided with a single large motor-generator set Ewhose motor I3 is powered by a source outside of the department andwhose generator H is of sumcient capacity to provide the power requiredby all of the mills and by the slitter. No other arrangement iseconomically practical.

The application of the principles of the present invention to thecold-rolling department represented by Figure l is shown "by Figure 2.The

generator I of the motor-generator set E is connected to power lines l5.These power lines power the various units in the department that areillustrated by Figure l as well as the other electrical equipmentnecessarily included by such a department but which is not illustrated.I

It is to be understood that practically all of the motors used in such adepartment are intended for D. C. current and include shunt-fieldwindings. mill of the type under discussion are compound 'wound sincethis provides for smoother rolling operations. Therefore, the wiringdiagram shows all of the'motors as being compound wound.

In the case of the mill A the armatures and series-field windings 2 and2 of all of the motors 2 are directly connected to the power lines ll.

Generally the motors of a continuous The shunt-fields 2 of these motorsare provided with controlling rheostats 2' so that their strength can bevaried. Before the present invention these shunt-fields were energizedby the lines II through a master rheostat connected in series with allof the shunt fields, the shunt fields themselves being connected inparallel relative to each other and the only way of simultaneouslyvarying thespeeds of all of the motors together was by means of thatmaster rheostat. The disadvantages of this procedure have already beendiscussed. s

In the present instance, however, the shunt-' fields 2 are connected bylines l6 to a generator II that is part of a small motor-generator setwhose motor I. .is connected through lines l9 to the lines l5 so as toreceive power from the motor-generator set that powers the entiredepartment. The generator i1 is provided'with a field winding Ilethat isenergized by the lines I 9 through a rheostat ll This motor-generator'set just described is of approximately no greater capacity than isrequired to properly energize all.

of the shunt-field windings 2 of the motors 2.

In other words, it is a very small aflair as com-.

pared to the set powering the entire department and is consequentlymuch'less expensive. Furthermore, it is to be noted that thismotor-gener ator set is entirely independent of the set powering theentire department so far as the operation of the latter is concerned.That is to say, variations in the output of the generator I! cannotpossibly afiect the output '0! the generator it.

If this were not so all of the other'electrical' equipment in thedepartment would'be affected.

In the case of the mill B the armature and series-field windings 6 and 6of the motor 6 are all directly energized by the generator I4 throughthe lines l5. This unit is likewise provided with a smallmotor-generator set whose generator 20 energizes the shunt-fieldwindings 6 of the motor 6 through lines 2|, the shuntfield rheostats 6of these motors 6 serving as controls. The motor 22 of this little motorgenerator-set is powered by the lines l5 through lines 23 and thefleld20 of the generator of this set is energized by these lines 23 through arheostat 20 The operation of these two mills will now. be described, itbeing kept in mind that they are two diil'erent units entirelyindependent of one another.

To'efiect threading of the mill A the rheostat I'l is adjusted so as toincrease the strength of the field ll of the generator IT. Thiscauses-the motors 2 to operate at sufiiciently slow speeds to permitmanual threading of the various ro lstands of this mill. When this iscompleted the rheostats- 2 are, adjusted toobtain the proper speedratios between the various motors powering the various stands so as tocompensate for the elongation of the work. As soon as this is done the"rheostat ll is operated to decrease the field strength of the generatorll, whereupon the B are each provided with a suitable electrical controlwhich permits these mills to be operatively independent of one anotherand which at the same time does not involve the great expense of theWard-Leonard system. The motor-generator. sets consisting of the motorsl8 and 22 and the generators l1 and 20 are sufilciently small to renderthe control economically practical. Upkeep is inexpensive and noelectrical complications are involved.

Now in the case of the mill the armatures I0 and series-fields Iii ofthe various roll-stand motors in, are all directly connected to thepower lines IS. The shunt-fields 1 and individual rheostats Iii of thevarious motors in, are connected to the power lines l5 through a masterrheostat 24.

To operate the mill C it is necessary to adjust the rheostat 24 toobtain the slow speeds that permit threading, the rheostats Hi beingadjusted to compensate for the elongation oi the work and the rheostat25 then set to accelerate the mill. This provides for reasonably goodoperation so long as all three of the roll stands of the mill C areused. However, it is often desirable to use less than all of these rollstands, and it is then necessary to eliminate one of the motors Hi. Thisremoves the rheostat ill of that motor and the motor itself from thecircuit, and the settings of the rheostat 24 are then no longer anindication of the speed of the mill.

It is to be understood that the controller elements of these rheostatsare marked to indicate threading and full rolling speeds, and are reliedupon by the rollers during the operation of the mill. Therefore, unlessa suitable additional resistance is put into the circuit by means of themaster rheostat to take the place of the omitted equipment, the rollerscannot properly operate the mill. As previously mentioned, it frequentlyhappens that carelessness in this respect leads to serious accidents. 7

The armature I2 series-field l2 and shuntfield ii of the slitters motorl2 are shown as being connected to the power lines i 5 in the usualmanner. trate the fact that the'cold-rolling department not onlyincludes anumber of mills but also other-electrical equipment.

The mill C is included partly to emphasize the fact that the departmentincludes a number of unit mills and partly to illustrate thedeficiencies of the old arrangement. The outputs of the littlemotor-generator sets that are used to energize the shunt-windings oftheir motors are relatively constant regardless of the number ofshunt-fields energized so long as the outputs of these sets aresufiicient to properly energize all of the shunt fields of the motors ineach instance.

Although the various units have been described as being connecteddirectly to the power lines IE, it is to be appreciated that thebranches of these power lines leading to these units do not necessarilyhave the carrying capacity of the power This motor is included simply toillus-' lines themselves, since the latter must carry power to all ofthe electrical equipment of th entire department.

In spite of the advanced state of the electrical control art there is noinstance known to the pres ent inventor .where a plurality of motorswhich must be speeded or slowed in unison have been controlled by meansof a small motor-generator set which energizes the shunt-fields of thesemotors and which is entirely independent of the main power source whichpowers the armature circuits of the motors. So far asis known, theWard-Leonard system is the only fool-proof control, while the rheostatcontrol illustrated in the case of the mill 0 is the only controlsufficiently inexpensive to be used in a cold-rolling or similardepartment. As a matter of fact, the average control used in conjunctionwith a small mill unit having tandem roll-stands consists simply of therheostats which control the shunt-fields of these motors, no masterrheostat being used because of the dangers involved. Hence a length ofstrip is .frequently almost completely rolled before the shunt-fieldrheostats can be juggled to positions which provide for full rollingspeeds and at the same time compensate for the elongation of the work. A

There are, of course, variations of the Ward- Leonard system whichinclude a motor-generator set that powers the armature circuits of aseries of mills and which is provided with a field excitingmotor-generator set which is relatively small and which in someinstances energizes the shuntfields of the motors. This cannot be usedin a cold-rolling department for the reason that any variation in theoutput of the exciting motor-gen erator set not only varies theshunt-fields of the motors but varies the field of the generator of themotor-generator set that is powering the entire mill. This obviouslyvaries the output of the motor-generator set, and if this set were usedto power an entire cold-rolling department, which is the onlyeconomically possible arrangement, all of the other electrical equipmentof the department would be afiected and the entire department throwninto confusion.

I claim:

1. In a mill department, a continuous mill including a plurality oftandem roll-stands each provided with an electric driving motor having ashunt-field winding, other electrical equipment operatively independentof. said mill and said motors, a motor-generatorsetofsufhcientcapacityto electrically power said motors and said other equipment, power linesarranged to carry the output of said motor-generator set to the armaturewindings of said motors and to said other electrical equipment that isoperatively independent of said motors, whereby variations in the outputof said motor-generator set will affect said motors and said otherelectrical equipment as well, a motor-generator set of approximately nogreater capacity than is required to properly energize the saidshunt-fleldwindings. of said motors, means for electrically connectingthe motor of the second named motor-generator set to said power lines,said second named motor-generator set being otherwise entirelyindependent of the first named motor-generator set, electric linesarranged to carry the output of said second named motor-generator set tosaid shunt-field windings o1. said'motors, variable resistances arrangedin said lines so as to individually control the energizingcurrentsupplied each of said shunt-field windings of said motors, and means iorvarying the output of said second named motor-generator set,.whereby thespeeds of said motors may be simultaneously varied without substantiallyaiiecting their respective speed ratios and without materially aflectingsaid other electrical equipment or said first named motorgenerator set.

2. A method of controlling the speeds of a plurality oi. tandemroll-stands driven by electric motors having shunt-field windings andpowered by a source that also powers other electrical equipment wherebyits output cannot be varied without afl'ecting the latter. saidshunt-field windings being each provided with variable reangerssistances, said method including powering the armaturea oi said motordirectly by said source. energizing said shunt-field windings throughsaid resistances by means 01 a second source whose output maybe variedwithout materially aflecting the output of the first named source,varying said resistances to obtain the speed ratios between said motorsrequired for the proper operation ofv said roll-stands and varying theoutput 01' said secondsource as required to cause said motors to drivesaid roll-stands at slow or threading speeds and to subsequentlyaccelerate so as to drive said roll-stands at fast or rolling speeds.-

' MARQUART.

